Waking up at night suddenly because of a bad dream can be terrifying. For many people, it is a nightmare, but for some, it’s a night terror. And if these dreams keep repeating, it’s important to know the difference between the two so it can be treated.

Nightmares are pretty common and are known as “bad dreams” with disturbing and vivid content. When you awaken from these bad dreams you usually have a memory of what happened and have a hard time falling back to sleep. Nightmares can leave you feeling a large range of emotions including sadness, depression, fear, guilt, and anger. Many of them tend to have common themes, such as going to school or work naked, suddenly losing your teeth, and being chased.

Nightmares usually occur after about an hour and a half of sleeping or in the latter part of the night during REM sleep. These bad dreams can be long and drawn out, and you may not remember the dream when you wake, but many people do have a recollection.

Night terrors, sometimes called ‘sleep terrors’, on the other hand, tend to happen in the deep stages of sleep, many times within the first hour, during non-REM sleep. They’re not “bad dreams”, but include arousal with extreme fear, agitation, large pupils, sweating, increased blood pressure and heart rate, screaming, crying, and feeling terrified for several minutes before eventually relaxing and falling back to sleep. For some people, night terrors are combined with sleep walking. When sufferers of night terrors awaken, many times they have no recollection of the event, or just a vague memory and are often confused.

The exact cause for night terrors is not well understood and is often misdiagnosed as nightmares or post-traumatic stress disorder (PTSD). For some patients, the terrors may be linked to medications for neurological disorders. Night terrors may also be brought on by sleep deprivation, stress, fever, lights, noise, and sleeping in an unfamiliar setting. They may also be associated with disorders such as obstructive sleep apnea (OSA), restless leg syndrome (RLS), migraines, and head injury. Research also shows they tend to run in families.

Some patients can even predict when these events will occur. For example, they know it happens about a half hour into sleep every night, and some may not recall any event the next morning.

Night terrors are more common in children ages 3-5 but can also happen to adults. If you think your child or loved one may have night terrors, some signs to look for include suddenly sitting up in the bed, screaming, shouting, kicking, thrashing, sweating, heavy breathing, and racing heart rate. Some people show aggressive behavior. They may also be hard to awaken, but if they are awake may seem confused and inconsolable.

If someone in your family is suffering from night terrors, the best thing you can do is comfort them. To keep them and yourself safe, make sure you keep any objects away from them that may be harmful when they’re panicked and in a sleeping state.

It’s important to contact the doctor if these episodes become more frequent, don’t seem to go away, if it routinely disrupts sleep, leads to dangerous behavior, follows a pattern, or begins in adulthood. A sleep study may be needed for diagnosis. If not treated, it can lead to disruptions to family in the house, embarrassment, even injury to the patient or anyone else around. It can also cause excessive daytime sleepiness, which can lead to difficulties in work and school, ultimately harming the quality of life.